To make a polarizing sheet, generally a polarizing film that is obtained by absorbing or impregnating iodine or dichroic dyes into a monoaxially starched polyvinyl alcohol (PVA) film is used. Generally, transparent resins, such as triacetylcellulose, are used on one or both sides of the polarizing film as a protective layer to make a polarizing plate. Such a polarizing plate is easily handled and is useful for secondary processing. Further, it is cheap and light.
The polarizing sheet is obtained by affixing a transparent resin sheet such as an aromatic polycarbonate sheet as a protective layer on both sides of a polarizing film (hereafter, the “polarizing sheet”). Generally, the film is a stretched polyvinyl alcohol film dyed with dichroic dyes. The polarizing sheet, which is obtained by a curving process, an injection process, or both, is used in polarizing lenses for sunglasses or goggles. Depending on the properties of the resin, for example, if the resin is an aromatic polycarbonate, the sunglasses or the goggles have superior impact resistance, as well as high heat resistance.
In the case of sunglasses and goggles that require impact resistance and heat resistance, the aromatic polycarbonate that is derived from bisphenol A is suitably used. However, since the aromatic polycarbonate has a large photoelastic constant, if the aromatic polycarbonate is curved to make a spherical or aspherical surface, such as in sunglasses or goggles, interference fringes in coloration easily arise by the retardation of the polycarbonate, and as a result, the interference fringes cause problems such as deterioration in the appearance of articles and eyestrain.
Further, in a polarizing lens obtained by curving a polarizing sheet that uses an aromatic polycarbonate as a transparent sheet to make spherical or aspherical surfaces, because of unevenness of the thickness of the aromatic polycarbonate polarizing sheet, distortion of images occurs. Therefore, the polarizing lens has problems in terms of causing deterioration in appearance (of articles) and eyestrain.
For retardation that arises during the curving processes, the aromatic polycarbonate sheet that is used as a protective layer subjected to pre-extruding to make an aromatic polycarbonate sheet with invisible interference fringes in coloration as a result of the large retardation (hereafter referred to as a “stretched polycarbonate polarizing sheet”) was known (Reference 1). Among various polarizing sheets, this sheet is used for articles that require an excellent appearance or that need to be very eye-friendly.
Further, in terms of improving the function of a polarizing lens that is obtained by curving the polarizing sheet, a polarizing lens that is obtained by curving a polarizing sheet to form a spherical or aspherical surface, inserting the curved polarizing sheet into a mold, and injecting a transparent resin to the mold to produce the lens (hereafter, “injecting polarizing lens”), is known. A polarizing lens that uses an aromatic polycarbonate as a resin is also known (hereafter “aromatic polycarbonate polarizing lens”) (References 2 and 3).
The aromatic polycarbonate polarizing lens is made by injecting an aromatic polycarbonate into a mold to fill the aromatic polycarbonate [in the concave surface of the curved aromatic polycarbonate sheet]. This brings about a benefit wherein the unevenness of the thickness of the stretched polycarbonate sheet that is inserted in the mold disappears. Thus, even for lenses without focus refractivity, they are used in products that require particularly excellent impact resistance or appearance or that need to be very eye-friendly.
In lenses such as aromatic polycarbonate polarizing lenses, which are obtained by inserting thermosetting resins or thermoplastic resins into molds, the shape and thickness of the molded lenses can be freely set by setting the shape of the surface of both sides of the mold and the distance between the two sides accordingly. Thus, based on the optical design, the shape and the distance between the two sides of the mold can be set so as to have the desired values of focus refractivity, prism-diopter, and image distortion.
The surface shape of the molded lens and the surface shape of the mold at the time of contact with the molded lens are generally identical. However, if a very high level of precision of the surface shape of the lens is required, to compensate for a reduction in the thickness of the lens or a change in the surface shape, which are caused by shrinking of the volume when thermosetting resins or thermoplastic resins that are injected into molds solidify, the surface shape and the distance between the two sides of the mold should be adjusted accordingly.
The surface of the injecting polarizing lens that is produced in this way is subjected to further appropriate steps, such as forming a hard coat layer or an anti-reflection film, etc., and then polishing the rims of the lenses, drilling, screw fastening, etc., to fix the lens to the frame, thereby making sunglasses and goggles.
In the polarizing lens obtained by applying curving processes to the polarizing sheet to form a spherical or aspherical surface or the injecting polarizing lens obtained by injecting aromatic polycarbonate, etc., for the purpose of reducing the glare of the surface of glass, the surface of water, etc., polarized light in the horizontal direction is cut. In addition, for the purpose of improving visibility or design, for example, an aromatic polycarbonate polarizing sheet colored in grey, brown, or the like, is used to provide a desired color tone and transmittance.
In order to increase the degree of polarization of a polarizing lens, the amount of dichroic dye for dyeing a polyvinyl alcohol film is adjusted to a concentration at which the polarization component in the horizontal direction of light incident on the polarizing lens is almost absorbed. And when the amount of the dichroic dye for dyeing the polyvinyl alcohol film is further increased, the polarization component in the perpendicular direction of light incident on the polarizing lens is also absorbed in a large amount. For a higher performing polarizing lens, a polarizing lens that shows decreased absorbance of the polarization component in the perpendicular direction of light incident in the polarizing lens, by using a dichroic dye that shows a higher dichroic ratio, is required.
Further, regarding the dichroic dyes for dyeing the polyvinyl alcohol film, not a single color, but several colors of dichroic dyes are used. In this regard, by changing the amount of each dichroic dye for dyeing the polyvinyl alcohol film, a polarizing lens having a desired color tone and transmittance can be obtained. Further, a method to obtain a polarizing lens that has a color tone or transmittance of interest by dissolving the dyes in an adhesive layer or an aromatic polycarbonate sheet can be used. The method can control the color tone or the transmittance of an injecting polarizing sheet by itself or in combination with the steps explained above.